Some main categories are:
Addition reactions for example the Aldol reaction and Michael reaction
Substitution notably coupling reactions. Ferric chloride is a well known catalyst in the Friedel–Crafts reaction. Compounds of the type [(η3-allyl)Fe(CO)4+X− are allyl cation synthons in allylic substitution. Likewise the compound Ph(CO2)Fe+(η2-vinyl(OEt))BF4− is a masked vinyl cation. Disodium tetracarbonylferrate can be regarded a CO dianion synthon.
Cycloadditions, for example cyclopropanation using CpFe(CO)2CH2S+(CH3)2BF4−.
Also Ene reaction Hydrogenation and reduction, example catalyst Knölker complex. Isomerization reactions and rearrangement reactions
Cross-coupling reactions. Iron compounds such as Fe(acac)3 catalyze a wide range of cross-coupling reactions with one substrate an aryl or alkyl Grignard and the other substrate an aryl, alkenyl (vinyl), or acyl organohalide. In the related Kumada coupling the catalysts are based on palladium and nickel.
Coupling reaction. A coupling reaction in organic chemistry is a general term for a variety of reactions where two hydrocarbon fragments are coupled with the aid of a metal catalyst.
In one important reaction type a main group organometallic compound of the type RM (R = organic fragment, M = main group centre) reacts with an organic halide of the type R'X with formation of a new carbon-carbon bond in the product R-R'  Broadly speaking, two types of coupling reactions are recognized: cross couplings involve reactions between two different partners, for example bromobenzene (PhBr) and vinyl chloride to give styrene (PhCH=CH2).homocouplings couple two identical partners, for example, the conversion of iodobenzene (PhI) to biphenyl (Ph-Ph).
Mechanism The reaction mechanism usually begins with oxidative addition of one organic halide to the catalyst. Catalysts Leaving groups The leaving group X in the organic partner is usually bromide, iodide or triflate. Rearrangement reaction. A rearrangement reaction is a broad class of organic reactions where the carbon skeleton of a molecule is rearranged to give a structural isomer of the original molecule. Often a substituent moves from one atom to another atom in the same molecule.
In the example below the substituent R moves from carbon atom 1 to carbon atom 2: Intermolecular rearrangements also take place. A rearrangement is not well represented by simple and discrete electron transfers (represented by curly arrows in organic chemistry texts). The actual mechanism of alkyl groups moving, as in Wagner-Meerwein rearrangement, probably involves transfer of the moving alkyl group fluidly along a bond, not ionic bond-breaking and forming. In pericyclic reactions, explanation by orbital interactions give a better picture than simple discrete electron transfers.
Three key rearrangement reactions are 1,2-rearrangements, pericyclic reactions and olefin metathesis. 1,2-rearrangements and the Beckmann rearrangement: Isomer. This article is about the chemical concept.
For "isomerism" of atomic nuclei, see nuclear isomer. An isomer (/ˈaɪsəmər/; from Greek ἰσομερής, isomerès; isos = "equal", méros = "part") is a molecule with the same chemical formula as another molecule, but with a different chemical structure. That is, isomers contain the same number of atoms of each element, but have different arrangements of their atoms. Isomers do not necessarily share similar properties, unless they also have the same functional groups.
There are many different classes of isomers, like positional isomers, cis-trans isomers and enantiomers, etc. (see chart below). Structural isomers The different types of isomers, including position isomers 2-fluoropropane and 1-fluoropropane on the left In structural isomers, sometimes referred to as constitutional isomers, the atoms and functional groups are joined together in different ways. Hydrogenation. Because of the importance of hydrogen, many related reactions have been developed for its use.
Most hydrogenations use gaseous hydrogen (H2), but some involve the alternative sources of hydrogen, not H2: these processes are called transfer hydrogenations. The reverse reaction, removal of hydrogen from a molecule, is called dehydrogenation. A reaction where bonds are broken while hydrogen is added is called hydrogenolysis, a reaction that may occur to carbon-carbon and carbon-heteroatom (oxygen, nitrogen or halogen) bonds. Hydrogenation differs from protonation or hydride addition: in hydrogenation, the products have the same charge as the reactants. Hydrogenation of unsaturated fats produces saturated fats. Cycloaddition. Ene reaction. The ene reaction (also known as the Alder-ene reaction) is a chemical reaction between an alkene with an allylic hydrogen (the ene) and a compound containing a multiple bond (the enophile), in order to form a new σ-bond with migration of the ene double bond and 1,5 hydrogen shift.
The product is a substituted alkene with the double bond shifted to the allylic position. Figure 1. The ene reaction This transformation is a group transfer pericyclic reaction, and therefore, usually requires highly activated substrates and/or high temperatures. Nonetheless, the reaction is compatible with a wide variety of functional groups that can be appended to the ene and enophile moieties. Also,many useful Lewis acid-catalyzed ene reactions have been developed which can afford high yields and selectivities at significantly lower temperatures, making the ene reaction a useful C–C forming tool for the synthesis of complex molecules and natural products. Substitution reaction. Substitution reaction (also known as single displacement reaction or single replacement reaction) is a chemical reaction during which one functional group in a chemical compound is replaced by another functional group. Substitution reactions are of prime importance in organic chemistry.
Substitution reactions in organic chemistry are classified either as electrophilic or nucleophilic depending upon the reagent involved. There are other classifications as well that are mentioned below. Michael reaction. The Michael reaction or Michael addition is the nucleophilic addition of a carbanion or another nucleophile to an α,β-unsaturated carbonyl compound.
It belongs to the larger class of conjugate additions. This is one of the most useful methods for the mild formation of C–C bonds. Many asymmetric variants exist. Definition As originally defined by Arthur Michael, the reaction is the addition of an enolate of a ketone or aldehyde to an α,β-unsaturated carbonyl compound at the β carbon. A newer definition, proposed by Kohler, is the 1,4-addition of a doubly stabilized carbon nucleophile to an α,β-unsaturated carbonyl compound. The Michael addition is an important atom-economical method for diastereoselective and enantioselective C–C bond formation. Aldol reaction. The aldol reaction is a means of forming carbon–carbon bonds in organic chemistry. Discovered independently by Charles-Adolphe Wurtz and Alexander Borodin in 1872, the reaction combines two carbonyl compounds (the original experiments used aldehydes) to form a new β-hydroxy carbonyl compound.
These products are known as aldols, from the aldehyde + alcohol, a structural motif seen in many of the products. Aldol structural units are found in many important molecules, whether naturally occurring or synthetic. For example, the aldol reaction has been used in the large-scale production of the commodity chemical pentaerythritol and the synthesis of the heart disease drug Lipitor (atorvastatin, calcium salt). The aldol reaction unites two relatively simple molecules into a more complex one. For example, stereogenic aldol units are especially common in polyketides, a class of molecules found in biological organisms.
Addition reaction. Addition of chlorine to ethylene An addition reaction, in organic chemistry, is in its simplest terms an organic reaction where two or more molecules combine to form a larger one (the adduct). Addition reactions are limited to chemical compounds that have multiple bonds, such as molecules with carbon-carbon double bonds (alkenes), or with triple bonds (alkynes).
Molecules containing carbon—hetero double bonds like carbonyl (C=O) groups, or imine (C=N) groups, can undergo addition as they too have double bond character.